Scalable virtual traffic hub interconnecting isolated networks

A system, comprising:

• one or more computing devices of a packet processing service of a provider network;
• wherein the one or more computing devices include instructions that upon execution on a processor cause the one or more computing devices to:
• in response to a programmatic request to configure a first virtual traffic hub as an intermediary for network traffic between a plurality of isolated networks, store metadata indicating (a) at least a first action implementation node assigned to the first virtual traffic hub, and (b) at least a first routing decision master node assigned to the first virtual traffic hub;
• propagate, to the first routing decision master node, respective sets of state information entries for a first isolated network;
• obtain, at the first action implementation node, a first executable action from the first routing decision master node, wherein the first executable action is to be implemented for one or more packets of a first network flow, wherein the first executable action is generated at the first routing decision master node based at least in part on the respective sets of state information entries, and wherein an indication of semantics of the first executable action is not provided to the first action implementation node;
• store, in a flow-indexed cache of the first action implementation node, the first executable action;
• cause, based at least in part on implementing the first executable action at the first routing action implementation node, contents of one or more data packets of the first network flow to be transmitted to a second isolated network.